1. Field of the Invention
The present invention involves materials, methods, and apparatus for adhering and conforming flexible films to substrates.
2. Description of the Related Art
Adherent films find many uses in modern commerce. For example, large graphic images used in advertising and other public displays are printed on films adhered to walls and other surfaces by means of pressure activated adhesives or other adhering means. As used herein, the term adherent films will mean films that can be adhered to a surface as a result of contact with that surface. Adherent films may comprise an adhesive surface, an electrostatic cling surface, or other adhering means that preferably involve intimate surface contact. A common type of adherent surface is one produced by a pressure activated adhesive layer. As used herein, the term pressure activated adhesive will include conventional tacky pressure sensitive adhesives as well as adhesives that may contain particulates, adhesive microspheres, microreplicated topologies, or other like adhesive systems in which adhesion is initiated by pressure applied between the adhesive and the substrate to be adhered.
Since many of the surfaces to which adherent films are to be adhered contain protrusions, depressions, and other irregularities, it is useful for such adherent films to be conformable to such surfaces. Conformability may arise from the inherent flexibility of the adherent film at room temperature, or may be produced by heating, as can be done when the adherent films are thermoplastic. It is common practice in the installation of such materials to first laminate the thermoplastic adherent film to a surface using reasonable care to produce a smooth lamination, without wrinkles, allowing tenting of the adherent film over protrusions and bridging of the adherent film over depressions. This initial lamination is then followed by selective heating of the adherent film in areas of surface irregularity, while applying pressure with resilient tools such as pads and brushes, to conform the adherent film to the surface. As used herein, the term tenting will mean the detachment of adherent film in the region surrounding a substrate protrusion which results in a tent-like draping of the adherent film over the protrusion. Similarly, the term bridging will mean the detachment of an adherent film as it is stretched over a depression in a substrate. It is common practice to pierce detached regions, for example bubbled, tented, or bridged areas, to allow release of entrapped air while pressing down on the detached region to produce conformance and adhesion. A useful tool for producing holes for the release of air is disclosed in U.S. Pat. No. 6,311,399, wherein resiliently mounted pins press against a laminated adherent film and penetrate the adherent film in areas of air entrapment, so as to provide paths for the release of entrapped air. Entrapped air in detached regions may also escape through channels within the adhesive layer. Adherent films such as 3M “Scotchcal” brand Marking film with “Comply” brand performance, commercially available from 3M Company, St. Paul, Minn., use microstructured channels, or microchannels, within the adhesive layer to allow the escape of entrapped air. Adhesive systems of this type are disclosed in co-assigned U.S. Pat. No. 6,197,397.
While various adhesive films have found wide commercial application, there remains a need for easier and faster methods of conforming such films to irregular substrates, for example riveted structures on semi-trailers and truck van bodies. Riveted structures tend to have large numbers of rivet heads requiring treatment to improve conformance, so that the speed of performing this operation becomes especially important. There is also a need for a method of conforming adherent films to irregular surfaces with less risk of damage to the surface of such films, such as might be caused by the brushes or pads commonly used to press heat-softened thermoplastic adherent films into conformance with irregular surfaces. Moreover, the current methods of conforming adherent films to irregular surfaces are often physically demanding, in that they require not only skill, but also a significant amount of physical strength and endurance. Additionally, current methods can be ergonomically demanding, in that they require simultaneous use of a heat source and several other tools, such as an air release tool for producing air release holes in the adherent film, along with a brush or pad for pressing the adherent film into contact with the surface. The task is made more difficult by the environment in which these tasks must be performed, namely standing next to the side of a semi-trailer or other large vertical surface, on a scaffold or other device providing elevation above floor level.